Tone control apparatus for electrical musical instruments



1951 E. MEINEMA 2,565,512

H. TONE CONTROL APPARATUS FOR ELECTRICAL MUSICAL INSTRUMENTS Filed June13, 1949 Herbe'rt Meinema Atty.

Patented Aug. 28, 1 951 TONE CONTROL APPARATUS FOR ELEC- TRICAL MUSICALINSTRUMENTS Herbert E. Meinema, Chicago, Ill., assignor t HammondInstrument Company, Chicago, 111., a corporation of Delaware ApplicationJune 13, 1949, Serial No. 98,684

6 Claims.

My invention relates generally to electrical musical instruments andmore particularly to improved means for controlling the tone quality ofan instrument of the electric organ type.

In electric organs constructed in the manner disclosed in the patent toLaurens Hammond No. 1,956,350, the selection of the quality of the tonesproduced is accomplished by individually controlling the amplitudes ofthe various partials. In said instrument, playing key operated switchesconnect the tone signal generators for the various partials respectivelyto bus-bars. The signals thus applied to the bus-bars are ofsubstantially equal amplitude and the Signals on these busbars aretransmitted to the output system through a transformer by selectivelyconnecting the busbars to various taps on the input side of thetransformer so as to regulate or predetermine the relative amplitudes ofthe partials. In said instrument these selective connections are made bymeans of drawbars which have spring contacts engageable with spacedcollector bars. In this construction, when the drawbars are adjusted thecontact With one of the collector bars is broken before contact was madewith another. This results in the production of clicks and otherundesired noises in the output system. It is therefore the object of myinvention to provide an improved drawbar construction whereby theadjustment of the drawbars may be effected without introducingtransients which might result in the production of noise in the outputof the instrument.

A further object is to provide an improved drawbar construction wherebyeach drawbar is provided with a pair of spaced contacts which areconnected by a resistor of low value, the contacts being spacedsufilciently apart relative to the spacing of the collector bars withwhich they contact that one of these contacts will at all times be incontact with one of the collector bars.

Other objects will appear from the following description, referencebeing had to the accompanying drawings in which:

Fig. l is a partly schematic view of the generating system of anelectric organ, showing a*por tion of the drawbar assembly infragmentary section;

Fig. 2 is a side elevational View of the drawbar assembly;

Fig. 3 is a fragmentary sectional view taken on line 33 of Fig. 1; and,

Fig. 4 is a bottom plan view of a portion of a drawbar contact mechanismwhich is shown in fundamental, the second, third, and fourth harmonicsof the note Al (110.000 c. p. s.), each of these generators comprising atone wheel l0 having the required number of high points and driven atthe speeds required to generate the frequencies of a 110, 220, 330, and440 c. p. s., or frequencies very close to these values. Generators 34and 46 are also utilized to supply the fundamental and second harmonicfrequencies for the note A2 of having a fundamental frequency of 220 c.p. s. It will be understood that the generators 22, 34, 4|, and 46 areintended to be representative of approximately generators each supplyinga substantially sine wave signal having a frequency required in theproduction of either the fundamental or one of the harmonic partials ofthe various notes of the musical scale Within the gamut of theinstrument.

Each of the generators has a permanent magnet |2 provided with awedge-shaped point l4 adjacent the periphery of the tone wheel. A pickupcoil [6 is wound on each of the permanent magnets l2 and has oneterminal grounded and the other connected through a capacitor IE to theungrounded terminal of the primary winding of a transformer 20. Theungrounded terminals of the secondaries of these transformers areconnected to switches 22 through parallel resistors 24, the impedance ofthese resistors being high with respect to the impedances of thegenerators to which they are connected.

The switches 22 are operable by the playing keys, such as the keys Aland A2, and are adapted to connect the generators to bus-bars 26. Theconnections between the generators and the switches 22 are such that,for example, the fundamental frequencies for the various tones will beimpressed on the first (uppermost) bus-bar 26, the second harmonics willbe impressed on the second bus-bar, etc.

The bus-bars 26 are connected respectively to drawbars 28 which aremounted for longitudinal sliding movement in a suitable drawbar housing30 having vertical panels 32, of insulating material, which are suitablyslotted to form guides for the drawbars.

The drawbars 28 have moulded plastic finger pieces 34 secured at theirforward ends, while their rearward ends, which project from the back ofthe housing 30, are bent downwardly at an angle and have spring fingers36 riveted thereto, each of these Spring fingers having a triangular endportion 38 which serves as a stop to limit the forward movement of thedrawbar to which it is attached. The end portions 38 also serve assolderi'ng lugs for the flexible wires 40 by which the' drawbars arerespectively connected to the busbars 26.

Each of the spring fingers 36 has a double contact assembly 42 securedat its free end. Each of these assemblies, as best shown in Figs. 3 and4, comprises insulating sheet 44 and d of mica, or the like, which aresecured to the spring finger by contact rivets 46, and 41. The rivet 46extends through both sheets 44 and 35, through a small bracket 48, andthrough an enlarged hole 49 in the spring finger 36, and is thuselectrically connected to the bracket 58 and insulated from the springfinger 36. The contact rivet 41 extends only through the insulatingsheet 45 and the spring finger 36 and is thus electrically connected tothe latter. The bracket 48 is located in proper position by a lug 5E)struck from the bracket and projecting through a suitably shaped opening51 formed in the insulating sheet 44.

The spring finger has a pair of protecting flanges 52 and an offset ear5d at its free end. A short length of wire 56, of a high resistancealloy, has its ends respectively welded to the bracket 43 and the ear54. The effective resistance of this wire may be approximately 1 ohm.

The contact rivets it and Marc adapted to make electric contact withspaced collector bars 58 which are inlaid in an insulating sheet 66secured within the housing 30. The bars 58 are so spaced with respect tothe spacing of the contact rivets 46, ll that at least one of the latterwill be held in electrical contact with one of the bars in everyposition to which the draw bar may be moved.

A tapered resistance element 622 is soldered to the bars 58, and isformed to provide progressively greater length portions thereof betweenthe bars 58. The element 62 is a very thin sheet of a high resistancealloy and its shape and conformation are such that the resistance itprovides between successive bars 58 increases substantiallylogarithmically from the rearmost to the foremost bar 58.

The rearmost bar 58 is connected to the grounded terminal of the primarywinding 64 of an output transformer 35 while the foremost bar 58 isconnected to the ungrounded terminal of this winding. The secondary 66of transformer '65 is connected to a preamplifier 68, which may includea suitable expression or volume control device. The preamplifier isconnected to a power amplifier it and the latter supplies a speaker 712.The resistance element 62 forms a voltage divider across the inputterminals of the transformer 65, and thus the amplitude of the signaltransmitted through the transformer is dependent upon which collectorbar '58 is connected by the drawbar 28 to the bus-bar 26.

Due to the resiliency of the spring fingers, at least one of the contactrivets 46, i? is maintained in contact with one of the collector bars 58at all times. When the contact rivets are in an intermediate position,in which they respectively contact adjacent bars 58, the resistance wire56 is connected across such bars and thus the portion of the resistanceelement "62 between these bars is not short-circuited. Instead theresistance between the two bars is decreased but the resistance isnevertheless sufficient to prevent spurious signals to pass from onebus-bar to the other and to avoid serious alterations in the graduatedresistances between the collector bars provided by the resistanceelement 62.

If the drawbars are shifted, even while a numtial transients will beproduced because the signal is continuously transmitted to the outputsystem through at least one of the collector bars 58. As the contacts ofthe drawbars are shifted from one collector bar to the next there is anintermediate position in which the signal is impressed on both collectorbars, but due to the provision of the resistance 56 the transition issmooth and clickless. Mechanical noises due to shifting the drawbars arealso substantially eliminated because it is not necessary that thedrawbars be held in any definite positions, and the spring fingers 36need not function as detents, as was necessary, or at least desirable,in prior constructions.

While I have shown and described a particular embodiment of myinvention, it will be apparent to those skilled in the art that numerousmodifications and variations may be made in the form and constructionthereof, without departing from the more fundamental principles of theinvention. I therefore desire, by the following claims, to includewithin the scope of my invention all such similar and modified forms ofthe apparatus disclosed, by which substantially the results of theinvention may be obtained by substantially the same or equivalent means.

I claim:

1. A drawbar assembly for the tone quality control of an electricalmusical instrument, comprising a plurality of spaced parallel collectorbars, a plurality of manually operable drawbars insulated from thecollector bars and movable transversely of the collector bars, a leafspring secured to each drawbar, a pair of contactors mounted on eachleaf spring for making sliding contact with the collector bars, saidcontactors being insulated from one another and spaced in the directionof movement of the drawbars a sufiicient distance to bridge the spacesbetween the collector bars, and a resistance element connected betweenthe contactors of each pair.

2. A drawbar assembly for the tone quality control of an electricalmusical instrument, comprising a plurality of spaced parallel collectorbars, a plurality of manually operable drawbars insulated from thecollector bars and movable transversely of the collector bars, a pair ofcontactors moved by each drawbar, resilient means to hold saidcontactors in position for making sliding contact with the collectorbars, said contactors being insulated from one another and spaced in thedirection of movement or" the drawbars a sufficient distance to bridgethe spaces between the collector bars, and a resistance elementconnected between the contactors of each pair.

3. In a tone quality control apparatus for an electrical musicalinstrument in .which playing keys operate switches respectively toconnect electric generators of the .partials of the tones to bus barsand in which an output system having a multi-tap coupling inputimpedance is employed, the combination of a plurality of manuallyadjustable control elements, a plurality of uniformly spaced collectorbars respectively connected to the taps on the coupling impedance, apair of contactors carried by each control element and cooperable withthe collector bars, said contactors being spaced relative to the spacingof the collector bars so that one of the contactors of each pair will atall times be in contact with one of the collector bars, meansrespectively conber of the playing keys are depressed, no substan- 15necting one contact on each control element to one of the bus bars, anda resistance interconnecting each pair of contactors.

4. In a tone quality control apparatus for an electrical musicalinstrument in which playing keys operate switches respectively toconnect electric generators of the partials of the tones to bus bars andin which an output system is provided, the combination of a couplinginput impedance, means to connect the coupling impedance with the inputof the output system, said impedance having a plurality of taps, aplurality of manually adjustable control elements, a plurality of spacedcollector bars respectively connected to the taps on said impedance, andcontactors carried by the control elements and cooperable with thecollector bars, said contactors being effective to bridge the spacesbetween adjacent collector bars so that at least one of the collectorbars will at all times be in contact with the contactors, saidcontactors offering sufficient resistance, when bridging the spacebetween adjacent collector bars, to prevent substantial shortcircuitingof the portion of the coupling impedance which is connected between suchcollector bars. and means for connecting the contactors respectivelywith the busbars.

5. An adjustable control apparatus for electrical musical instrumentscomprising, a plurality of spaced parallel collector bars, impedancemeans of graded low values respectively interconnecting said collectorbars, a plurality of drawbars mounted adjacent one another foradjustable sliding movement in a direction perpendicular to thecollector bars, a pair of contactors carried by each drawbar, resilientmeans urging the contactors toward the collector bars to make electricalcontact therewith, the spacing of the contactors being such relative tothe spacing of the collector bars that at least one contactor of eachpair is at all times in contact with one of the collector bars, andimpedances of low value respectively connecting the contactors of eachpair.

6. In a tone quality control apparatus for an electrical musicalinstrument in which playing keys operate switches respectively toconnect electric generators of the partials of the tones to bus bars andin which an output system is provided, the combination of a low valuecoupling input impedance, means to connect the coupling impedance withthe input of the output system, said impedance having a plurality oftaps, a plurality of manually adjustable control elements, a pluralityof spaced collector bars respectively connected to the taps on saidimpedance, a contacting device carried by each of the control elementsand cooperable with the collector bars, said devices being movable bythe drawbars in a direction transverse to the collector bars, being ofsufficient length in their direction of movement to bridge adjacentcollector bars, and affording sufficient electrical resistance whenbridging adjacent collector bars that the portion of the couplingimpedance between such adjacent collector bars is not effectivelyshortcircuited, and means for connecting the contacting devicesrespectively with the bus-bars.

HERBERT E. MEINEMA.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,956,350 Hammond Apr. 24, 19342,254,366 Hammond Sept. 2, 1941

